Hydraulic machines are commonly used in the areas of construction, mining, and excavation. In a typical mining and excavating operation, large hydraulic machinery fills a bucket with material, transports the bucket load to a truck or conveyer belt, and unloads the material into the truck bed or onto the belt. Such repetitive tasks are ideal candidates for increased productivity through automation.
Robotic systems are typically designed to perform tasks as efficiently as possible by optimizing performance criteria such as fuel consumption and time to complete a task. Robot motion planning systems may use dynamic models of the robot to determine non-linear effects and to plan optimal motion paths. Such a motion planning system may adjust the commands or paths of motion according to the simulated response of the robot. Simple linear models constructed to approximate the robot's response often fail to yield satisfactory results due to non-linear actuator interactions that are not represented in the simplified model. Non-linear models are more accurate, but it may be difficult to solve them in real-time with data processors that are feasible to use for these purposes. For example, a full analytical model of an automated excavator including linkage and actuator dynamics, is a coupled, eighth-order non-linear system of equations that requires several hours to solve on a microprocessor. The non-linearity is due not only to the dynamic coupling between the links of such a machine, but also to the coupling between the different actuators. The inter-actuator coupling is partly due to a single engine providing power to the machine, with the power demanded being frequently higher than the maximum output of the engine. It may also be partly due to the design of the hydraulic system itself, especially when one pump drives more than one actuator and can not supply full pressure to all of the actuators during high demand.
A variety of methods to model and simulate performance of electrically-driven actuators have been developed. A common approach is to model actuators with a transfer function from which output response may be computed for given input signals. This method is not suitable, however, to model systems that are subject to non-linear performance limitations and interactions that arise when two or more actuators are driven by the same hydraulic pump.
U.S. Pat. No. 5,182,908, issued to Devier et al. discloses the use of table-look-up functions to model a system for controlling a machine wherein several hydraulically actuated parts share the same fluid pump. The table look-up functions use multiple inputs to determine which of the actuators should be given priority while limiting flow to the others. The Devier et al. patent does not, however, teach a method for determining information that is required by motion planning algorithms such as the actual flow distribution to each of the actuators.
U.S. Pat. Nos. 4,712,376 and 5,167,121 disclose control systems where one hydraulic pump is used to drive two or more hydraulic actuators. The devices in these patents assume that the commanded fluid flow is provided to one of the actuators, while the remaining flow is used to drive the other actuator. These devices do not accommodate situations where two actuators require similar force at the same time, however.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.